ISTANBUL (AP) — Two explosions hit Saturday night outside a major soccer stadium in Istanbul, and Turkish authorities say about 20 police officers have been wounded.

Police cordoned off the area as smoke rose from the newly built Besiktas Stadium. Witnesses said gunfire could be heard in what appeared to have been an armed attack on police. The private NTV channel said the target of the attack was a bus for riot police.

There was no immediate claim of responsibility for the attack. This year Istanbul has witnessed bombings attributed by authorities to the Islamic State group or claimed by Kurdish militants.

Interior Minister Suleyman Soylu gave the casualty toll and said the wounded were police officers. The explosions took place after the home team Besiktas beat visitor Bursaspor 2-1 in the Turkish Super League.

“It is thought to be a car bomb at a point where our special forces police were located, right after the match at the exit where Bursaspor fans exited, after the fans had left,” Soylu was quoted as saying by Turkey’s state-run Anadolu Agency. “We have no information on the number of dead. God willing, we hope there won’t be any. The wounded are police.”

Television images showed more than a dozen ambulances on a street hugging the stadium and a police helicopter flying overhead with its searchlights on. The window glass of nearby buildings was shattered by the blasts and coated the pavement.

Bursaspor said none of the wounded were fans and issued a statement saying “we wish a speedy recovery to our wounded citizens.”